1. Field
The present disclosure relates to recombinant microorganisms with improved lactate production, and methods of producing lactic acid using the same.
2. Description of the Related Art
Lactic acid (also referred to as lactate) is being widely used in a variety of industries such as food, pharmaceutical, chemical, and electronic fields. Lactic acid is a colorless, odorless, and low-volatile substance that is easily soluble in water. Lactic acid that is not toxic to the human body is used as a flavoring agent, an acidifier, a preserving agent, or the like. Also, lactic acid is a raw material of biodegradable polylactic acid (PLA) that is an alternative environmentally friendly polymeric material.
Technically, PLA is a polyester-based resin that is obtained by conversion to lactide in the form of a dimer and then by ring-opening polymerization, and PLA is available in various processing forms such as film, sheet, fiber, injection, and the like. Therefore, there has recently been increasing demand for PLA as a bio-plastic that may widely replace existing general-purpose petrochemical plastics such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), or the like.
In addition, lactic acid has a hydroxyl group and a carboxyl group at the same time and, thus, it is very reactive. Accordingly, lactic acid may be readily converted to an industrially important compound such as lactic acid ester, acetaldehyde, propylene glycol, or the like. Thus, lactic acid is in the spotlight as an alternative next generation raw chemical material in the field of chemical industry, as well.
In terms of modern industry, lactic acid is produced by a process of petrochemical synthesis and biotechnological fermentation. The petrochemical synthesis is carried out by oxidizing ethylene derived from crude oil, obtaining lactonitrile through acetaldehyde by adding hydrogen cyanide thereto, distilling for purification, and hydrolyzing the reaction product using hydrochloric acid or sulfuric acid to produce lactic acid. The biotechnological fermentation is carried out by using a renewable carbohydrate such as starch, sucrose, maltose, glucose, fructose, and xylose, as a substrate to produce lactic acid.
When a substance that may be obtained by a general chemistry reaction formula in several steps is produced using microorganisms, the substance may be produced more efficiently. Here, the substance is produced more efficiently than in general chemical synthesis in terms of cost and time, and thus there have been many studies using microorganisms. However, microorganisms do not produce only certain metabolites and, if certain metabolites are produced excessively, microbial growth is rather inhibited or the metabolite is no longer produced. Instead, useless byproducts may be produced. Therefore, it is urgent to solve the above-described problems and develop a strain that efficiently produces lactic acid.